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Hongshun YANG

National University of Singapore, Food Science and Technology Programme, Faculty Member

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My overall research interests are sustainable food processing and safety engineering. Our mission is to improve the sustainability and safety of food production through applying processing and engineering knowledge and technology, and develop rapid detection and processing technology for detecting and controlling hazards unintentionally or intentionally added into food supply chain. The goal of our research is to provide valid solutions to improve our capability in food security and defense in addition to sustainability.
Phone: 65-96439328
Address: http://nusfood.wixsite.com/yanghs
http://www.fst.nus.edu.sg/OurPeople/YangHS.html

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Raphaël E Duval

Université de Lorraine

Sebastian Aguayo

Swinburne University of Technology, Hawthorn

Russell Crawford

Swinburne University of Technology

Joseph Graves Jr

Swansea University

Ibtissem GAMMOUDI

Diana Swan S. Alves

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Papers by Hongshun YANG

Application of atomic force microscopy in food microorganisms

Background: Microorganisms play an important role in the food industry. Knowledge of the surface ... more Background: Microorganisms play an important role in the food industry. Knowledge of the surface structural and physical properties of food microorganism cells is crucial to gain a detailed understanding of their functions in the natural environment and to explore them efficiently in various food processes. Atomic force microscopy (AFM), as a non-invasive examination tool, has been widely used to image the surface ultrastructure and to probe the physical properties of food microorganisms. Scope and approach: In the current review, detailed applications of AFM in various food microorganisms are outlined, including surface imaging, biomolecular interactions, surface stiffness, and physicochemical properties , which have contributed to our knowledge of cell surface functions. The study emphasises the combination of AFM imaging with force determination, which added a new feature to the AFM technique; i.e., mapping of specific interactions. The combined use of AFM with other complementary techniques for a comprehensive description of cell surface is also reported. Conclusions: and key findings: AFM has given promising results and thus could be a powerful technique for surface characterisation at nanoscale resolution and could provide new insight into the structure-function relationship of microbial surfaces.

Accepted Manuscript Effects of κ-carrageenan on the structure and rheological properties of fish gelatin

Effects of κ-carrageenan on the structure and rheological properties of fish gelatin,

Impact of soybean protein isolate-chitosan edible coating on the softening of apricot fruit during storage

A soybean protein isolate (SPI)-chitosan edible coating was used to prolong the shelf life of apr... more A soybean protein isolate (SPI)-chitosan edible coating was used to prolong the shelf life of apricots stored at 2 °C. Apricots were coated with two different coating formulations (SPI and SPI combined with chitosan). The changes to several parameters including weight loss, firmness, titratable acidity, soluble solids content, pectin contents, and the nanostructural properties of pectin were investigated to evaluate the effectiveness of the coatings. The coatings, especially the SPI-chitosan coating, significantly decreased the weight loss of apricots. Meanwhile, this treatment prevented the decrease in firmness and benefited the textural properties of the tissue. The atomic force microscopy (AFM) results showed a greater F q (the percent of pectin chains of particular width or length among all the chains observed by AFM) for the width and length of pectin molecules in the SPI-chitosan coated samples (width ≥ 61 nm; length ≥ 3 μm), which indicated that the SPI-chitosan coating could inhibit pectin degradation. The results showed that the SPI-chitosan coating is an effective method to preserve the quality of apricots.

Effects of Vacuum Impregnation with Calcium Ascorbate and Disodium Stannous Citrate on Chinese Red Bayberry

This study aimed to improve the shelf life of Chinese red bayberries using vacuum impregnation. V... more This study aimed to improve the shelf life of Chinese red bayberries using vacuum impregnation. Vacuum pressure of 5 kPa for 15 min, atmospheric pressure for 10 min, an impregnation temperature of 20 °C, alone or in combination with isotonic sucrose solution, 1% food-grade disodium stannous citrate (DSC) and 2% food-grade calcium ascorbate were used for vacuum impreg-nation. Quality parameters, including firmness, weight loss, decay rate, microbial counts and polyphenol oxidase (PPO) and peroxidase (POD) activities, of red bayberries were studied at 2 °C for 10 days. The monosaccharide components, chemical structures and nanostructure properties of chelate-soluble pectin (CSP) were further studied using high-performance liquid chromatography, Fourier transform infrared spectroscopy and atomic force microscopy (AFM). The results indicated that vacuum impregnation with calcium ascorbate alone or calcium ascorbate combined with DSC showed significant effects on inhibiting the decrease of firmness (4–10 days), the increase of weight loss (2–10 days), decay rate (4–10 days) and microbial growth (2–10 days). In addition, vacuum impregnation with single calcium ascorbate or DSC or their combination significantly inhibited the increase of colour difference from day 6 to day 10 during storage, which was better than atmospheric impregnation. Furthermore, vacuum impregnation with DSC and calcium ascorbate had the best effect on sensory attributes. The nanostructure analysis by AFM showed CSP of large width and length when calcium ascorbate was impregnated, suggesting that vacuum impregnated with 2% calcium ascorbate inhibited the degradation and dissociation of CSP, although these fruits showed more branching of rhamnogalacturonan and a small change in chemical structure.

sup-0002-FigS2.doc

Structural Modification of Fish Gelatin by the Addition of Gellan, κ-Carrageenan, and Salts Mimics the Critical Physicochemical Properties of Pork Gelatin

Pork gelatin is not suitable for halal and kosher application; however, fish gelatin (FG) can be ... more Pork gelatin is not suitable for halal and kosher application; however, fish gelatin (FG) can be modified for use as a pork gelatin (PG) mimetic. Herein, low-acyl gellan (GE), κ-carrageenan (KC), and salts (CaCl 2 or KCl) were combined with a 180 Bloom tilapia FG. A formulation comprising 5.925% (w/v) FG + 0.025% (w/v) GE + 3mM CaCl 2 best matched the physicochemical properties of PG. The modification increased the FG gel strength from 115 ± 2 to 149 ± 2g (matching the 148 ± 2 of PG), while the T m increased from 27.9 ± 1.0 to 32.4 ± 0.8 °C (matching the 33.1 ± 0.3 °C of PG). Nanoaggregates (diameter between 150 and 300 nm) could be an important structural factor affecting the physicochemical properties, as both PG and GE-modified FG showed a similar frequency distribution in this size group (57.4 ± 1.6% (PG) compared with 56.3 ± 2.2% (modified FG)). To further explore the differences between KC and GE in modifying of FG's structure, the FG-KC and FG-GE gels were compared. The zeta potential and Fourier transform infrared (FTIR) spectroscopy results for the FG-KC gel supported an associative interaction with complex formation, as indicated from the large aggregates and amorphous phase under atomic force microscopy (AFM). Contrastingly, a segregative FG-GE interaction took place in presence of CaCl 2. These structures and interaction differences between FG-GE and FG-KC influenced the macro-properties of FG, possibly explaining the differences in the modification of the melting temperature of FG. A diagram representing the interaction-structure-physicochemical properties was proposed to explain the differences between the FG-GE and FG-KC gels. Practical Application: Certain people cannot consume any pork product or derivatives for religious reasons, thus it is essential to find a pork gelatin (PG) substitute for food product development. The commonly used polysaccharides, gellan and carrageenan, together with salt, can be added to fish gelatin (FG) to match the textural properties of PG, representing a promising substitute for PG. The difference in the mechanism of gellan and carrageenan to improve properties of FG has been revealed from nanostructure level. The use of food grade ingredients and simple mixing process are favorable in the food industry.

sup-0001-FigS1.doc

Characterisation of rheology and microstructures of κ-carrageenan in ethanol-water mixtures

A B S T R A C T The effects of ethanol (up to 20 wt%) on the rheological properties and structura... more A B S T R A C T The effects of ethanol (up to 20 wt%) on the rheological properties and structural characteristics of κ-carra-geenan gel were investigated by Field Emission Scanning Electron Microscopy (FESEM) and Small Angle X-ray Scattering (SAXS). Both the sol-gel and gel-sol transition temperatures shifted to higher degree (from 36.8 ± 0.5 to 52.5 ± 1.4 °C and from 51.2 ± 0.6 to 67.0 ± 0.5 °C, respectively) upon 20 wt% ethanol addition (P < 0.05). The critical relaxation exponent n and the critical gel strength S g obtained from Winter-Chambon criterion decreased and increased, respectively as the ethanol concentration increased. The κ-carrageenan gel was formed due to the formation of fibrillar networks, and the fibrillar density increased upon ethanol addition via FESEM. Moreover, upon 20 wt% ethanol addition, the average radius of gyration of κ-carrageenan strand increased from 1.18 ± 0.03 of control to 1.55 ± 0.02 nm by SAXS. A mechanism underlying the effect of ethanol on the κ-carrageenan gelation was proposed based on coil to double helix transition followed by the helix aggregation.

Effect of ultrasonic pretreatment on whey protein hydrolysis by alcalase: Thermodynamic parameters, physicochemical properties and bioactivities

A B S T R A C T The effects of ultrasonic pretreatment on the enzymolysis thermodynamics and phys... more A B S T R A C T The effects of ultrasonic pretreatment on the enzymolysis thermodynamics and physicochemical properties of whey protein, and the mechanisms behind those effects, were investigated. Changes in the angiotensin-I converting enzyme (ACE) inhibitory and immunomodulatory activities of whey protein hydrolysates after ultrasonic pretreatment were also determined. Results showed that the ultrasonicated whey protein had a higher in degree of hydrolysis than the non-sonicated protein. After the pretreatment, the activation energy (E a), enthalpy of activation (ΔH) and entropy of activation (ΔS) of whey protein enzymolysis were decreased by 15.9%, 16.8%, and 16.4%, respectively. There was no significant change in free energy (ΔG) (P > 0.05). Physicochemical analysis revealed that ultrasound had induced unfolding of the whey protein, resulting in a 43.7% increase in its surface free sulfhydryl content and a 62.6% increase in surface hydrophobicity. Ultrasound significantly decreased the protein's α-helical content and significantly increased its β-sheets and β-turns (P < 0.05). The ACE inhibitory and immunomodulatory activities of the whey protein hydrolysates were significantly increased by ultrasonic pretreatment (P < 0.05). These results suggest that ultrasound can be applied to enhance whey protein enzymolysis for the generation of novel bioactive peptides that can be used as drug or functional food ingredient.

Development of Portable Flow-Through Electrochemical Sanitizing Unit to Generate Near Neutral Electrolyzed Water

We developed a portable flow-through, electrochemical sanitizing unit to produce near neutral pH ... more We developed a portable flow-through, electrochemical sanitizing unit to produce near neutral pH electrolyzed water (producing NEW). Two methods of redirecting cathode yields back to the anode chamber and redirecting anode yields the cathode chamber were used. The NEW yields were evaluated, including: free available chlorine (FAC), oxidation-reduction potential (ORP), and pH. The performances of 2 electrodes (RuO 2-IrO 2 /TiO 2 and IrO 2-Ta 2 O 5 /TiO 2) were investigated. The unit produced NEW at pH 6.46 to 7.17, an ORP of 805.5 to 895.8 mV, and FAC of 3.7 to 82.0 mg/L. The NEW produced by redirecting cathode yields had stronger bactericidal effects than the NEW produced by redirecting anode yields or NEW produced by mixing the commercial unit's anode and cathode product (P < 0.05). Electron spin resonance results showed hydroxyl free radicals and superoxide anion free radicals were present in the NEW produced by developed unit. The NEW generator is a promising sanitizing unit for consumers and the food industry to control foodborne pathogens. Practical Application: Current commercial NEW-producing units are quite large and are not convenient for family using. The developed portable flow-through, NEW-producing unit has great potential in a wide range of applications, such as organic farm, households, and small food industries. The examined sanitizing treatments showed effective control of Escherichia coli O157:H7 and Listeria monocytogenes.

Metabolite profiling of Listeria innocua for unravelling the inactivation mechanism of electrolysed water by nuclear magnetic resonance spectroscopy

A B S T R A C T Bactericidal effects of low concentration electrolysed water (LcEW) on microorgan... more A B S T R A C T Bactericidal effects of low concentration electrolysed water (LcEW) on microorganisms are previously well reported ; however, the inactivation mechanism of EW is not understood. The lethal and sublethal injuries of L. monocytogenes and L. innocua by EW treatments were determined and the metabolic profile changes for L. in-nocua were characterised using nuclear magnetic resonance (NMR). Microbial metabolomics approach combined with multivariate data analyses was used to interpret the cellular chemical fingerprints of L. innocua. The relative amount of intracellular reactive oxygen species (ROS) was assayed using 2′,7-dichlorodihydrofluorescein dia-cetate (H 2 DCFDA). The results showed that the proportion of the sublethally injured microbial cells L. mono-cytogenes and L. innocua increased from 40% to 70% and from 35% to 65%, respectively, when the free available chlorine (FAC) of LcEW increased from 2 to 8 mg/L. Overall, 36 low-molecular-weight metabolic compounds in L. innocua extracts were characterised by NMR spectroscopy. EW perturbation resulted in a drastic and multitude disruption across a wide range of biochemical process including peptidoglycan synthesis, nucleotides bio-synthesis and amino acid metabolism. Elevated levels of α-ketoglutarate and succinate implicated the enhanced glutamate decarboxylase (GAD) system and γ-aminobutyric acid (GABA) shunt for the protection against oxi-dative stress. These findings provided the comprehensive insights into the metabolic response of Listeria to EW oxidative stress and can serve as a basis for better utilisation for sanitisation.

Effect of exogenous ATP on the postharvest properties and pectin degradation of mung bean sprouts (Vigna radiata

A B S T R A C T The effects of exogenous ATP on the postharvest quality, browning and softening o... more A B S T R A C T The effects of exogenous ATP on the postharvest quality, browning and softening of mung bean (Vigna radiata) sprouts were evaluated. ATP treatment significantly alleviated the quality loss and browning events during the storage of 3 days. It also reduced the oxidant damage by inducing high activities of peroxidase (9.3–13.9%) and superoxide dismutase (8.8–10.3%) which scavenged the reactive oxygen species (ROS) effectively. Transcriptional results indicated that ATP treatment decreased VrPL1, VrPME and VrPG1 gene expression levels more than 2 folds at some time points. Furthermore, the atomic force microscope (AFM) images revealed that the pectin degradation was notably slowed by ATP treatment and the width and height of pectin backbone were better maintained (47.1% and 45.6% higher than control without ATP treatment). The cooperative effects of ROS scavenging and decreased expressions of pectin-related genes might contribute to the deferred pectin deterioration and firmness loss by ATP treatment.

Colourimetric detection of swine-specific DNA for halal authentication using gold nanoparticles

Detecting pork contamination is critical for halal food preparation. A fragment of species-specif... more Detecting pork contamination is critical for halal food preparation. A fragment of species-specific DNA from swine mitochondrial genome was selected as a target, and two oligonucleotides complementary to the target were used as probes for pork identification. The probe-conjugated gold nanoparticles bound to the target DNA, leading to the aggregation of gold nanoparticles and thus causing the colour of the gold nanoparticles to change from red to blue. More than 0.1 mmol/L of DNA led to an obvious colour change, which was observed by naked eyes after dotting test solutions onto a thin layer chromatography (TLC) plate. Furthermore, 0.001e1 mmol/L of the target was semi-quantified by using a digital camera and image processing software. This colourimetric detection might be a promising technique for differentiation of pork from other animal meat products without using any sophisticated machines, and thus will be used for halal authentication.

Effects of sucrose addition on the rheology and microstructure of k-carrageenan gel

The thermoreversible gelation behaviour of aqueous k-carrageenan solution with addition of sucros... more The thermoreversible gelation behaviour of aqueous k-carrageenan solution with addition of sucrose (up to 30 wt%) was investigated via small and large deformation oscillatory rheology. The structures of these k-carrageenan/sucrose gels were characterised by Fourier transform infrared (FTIR) spectroscopy, small angle X-ray scattering (SAXS) and field emission scanning electron microscopy (FESEM). Incorporation of 30 wt% sucrose shifted both the gelation temperature (from 36.8 C to 52.8 C) and melting temperature (from 51.2 C to 67.3 C) to a higher level and made gel network stronger. The critical relaxation exponent n, critical gel strength S g and normalised S g obtained from Winter-Chambon equation varied as the concentration of sucrose increased. More specifically, with an increased addition of sucrose, n decreased while both S g and normalised S g increased. The shift of FTIR band of G4S in k-carrageenan and loss of the vibration band of free hydroxyl group in sucrose indicated the interactions between sucrose and k-carrageenan molecules. SAXS and FESEM results supported the rheology findings and revealed that denser and thicker carrageenan fibril structures formed when addition of sucrose increased. Moreover, upon 30 wt% sucrose, the average cross-sectional radius of gyration R c of the carrageenan chains increased from 1.17 to 1.47 nm. In summary, a scheme was proposed to demonstrate how sucrose addition promoted the gelation of k-carrageenan by facilitating the formation of denser and thicker fibril helical junctions.

Comparative study of pyrethroids residue in fruit peels and fleshes using polystyrene-coated magnetic nanoparticles based clean-up techniques

An efficient and rapid method for quantifying pyrethroids pesticide residue in fruits samples was... more An efficient and rapid method for quantifying pyrethroids pesticide residue in fruits samples was developed in the present study. The application of lab prepared polystyrene magnetic nanoparticles based magnetic solid phase extraction technique combined with liquid-solid extraction helped clean-up the sample and preconcentrate the targeted analytes prior to HPLC quantification. The lab prepared nanoparticles were characterised with Fourier transform infrared spectroscopy, atomic force microscopy, X-ray diffraction spectroscopy, as well as vibrating sample magnetometer to study their size, morphology, crystal structure, functional groups and magnetism properties, respectively. Afterwards, optimisation of the parameters affecting extraction efficiency was carried out in order to achieve optimum conditions for extracting pyrethroids residue from fruit samples. Analytical performances were evaluated by carrying out experiments at optimum conditions. Results showed that the limit of detection and limit of quantification were below 0.1445 and 0.5116 ng g À1 , respectively for the six pyrethroids tested. The recovery rates were within the range of 73.6%e123.1% with intra-day and inter-day relative standard deviation being less than 16.5% and 15.4%, respectively, suggesting satisfactory reproducibility of the proposed method. Real sample analysis was performed using 6 kinds of commonly consumed fruits obtained from local supermarkets in Singapore, including apples, pears, oranges, lemons, grapes and nectarines. The peel and flesh were tested separately to study the difference of pyrethroids residue in different parts of fruits. The grape sample tested was detected with permethrin residue on its peel. There was no violation since the permethrin amount detected was way much lower than the maximum residue limit set by local government.

39-Figs S1-S3.docx

Supplementary Figure 1. ESI-MS and ESI-MS 2 spectra of two purified monomeric anthocyanins. Struc... more

Characterization and purification of anthocyanins from black peanut (Arachis hypogaea L.) skin by combined column chromatography

Journal of Chromatography A, 2017

Cyanidin-3-O-sambubioside Preparative ODS-AQ column HPLC-PDA-ESI–MS/MS NMR spectroscopy a b s t r... more Cyanidin-3-O-sambubioside Preparative ODS-AQ column HPLC-PDA-ESI–MS/MS NMR spectroscopy a b s t r a c t Black peanut skins as a byproduct from peanut industry contain abundant anthocyanins, evaluated as 8.61 ± 0.27 mg/g dry black peanut skins, are currently poorly exploited. In this work, four anthocyanins and three major flavonols were detected and identified by HPLC-PDA-ESI–MS/MS from the acidified water extract of black peanut skins of Arachis hypogaea L. After preliminary removal of flavonols by ethyl acetate (EtOAc), further purification of the anthocyanins was conducted using a combination of Amberlite XAD-7HP and ODS-AQ-HG column chromatography methods. Two most abundant monomeric anthocyanins cyanidin-3-O-sophoroside (5.77 ± 0.42 mg) and cyanidin-3-O-sambubioside (4.10 ± 0.17 mg) were eventually obtained from 2 g dry black peanut skins, and their purities were determined by HPLC-PDA as 97.29% and 98.28% at the yields of 87.47% and 64.27% on the basis of their total amount in the crude extracts, respectively. These sequential treatments can be easily adapted to large-scale fractionation of pure anthocyanin monomers.

Influence of chitosan-based coatings on the physicochemical properties and pectin nanostructure of Chinese cherry

A B S T R A C T The effects of chitosan-based coatings on the postharvest performance Chinese che... more A B S T R A C T The effects of chitosan-based coatings on the postharvest performance Chinese cherry during a twenty days storage period were investigated. The chitosan-based coatings effectively delayed postharvest ripening parameters including weight loss, decay rate, firmness, soluble solid content (SSC) and titratable acidity (TA). The most effective treatment was a combined chitosan and nano-SiOx coating, which led to 51% less weight loss, 32% less decay rate, 57% more firmness, and less SSC and TA content changes than the control group. This combined coating also maintained a higher content of sodium carbonate-soluble pectin (SSP), and inhibited pectin chain degradation. Qualitative and quantitative analysis revealed that the firmness of fruit was closely related to nanostructural morphologies and SSP chain width. In addition, modifications of SSP were correlated with fruit softening, especially SSP polymers and branched chains. These results demonstrate the effect of chitosan and nano-SiOx coating on extending the shelf life of Chinese cherries during postharvest storage.

Effects of Bromelain Tenderisation on Myofibrillar Proteins, Texture and Flavour of Fish Balls Prepared from Golden Pomfret

An enzymatic method to tenderise golden pomfret (GP, Trachinotus blochii) flesh by marinating wit... more An enzymatic method to tenderise golden pomfret (GP, Trachinotus blochii) flesh by marinating with bromelain (BML) solution was developed to produce GP fish balls with a texture similar to those of yellowtail fusilier (YF, Caesio cuning). Treatment with BML reduced the hardness, chewiness and gel strength significantly but increased the resilience of GP fish balls. As a result, 0.4% (enzyme-substrate ratio, w/w) BML-treated GP fish balls had the same texture properties as YF fish balls. Meanwhile, changes in myofibril-lar proteins in the fish balls were determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis, matrix-assisted laser desorption/ionisation time-of-flight mass spec-trometry and atomic force microscopy. The results indicated that BML degraded myosin light chain and troponin T effectively , without affecting actin. BML treatment generated protein fragments with significantly smaller sizes, thereby improving the tenderness of the flesh. The length, width and height of the myofibrils from 0.4% BML-treated fish ball were 6.42, 1.52 and 1.48 μm, respectively, which were not significantly different from the myofibrils of YF fish balls, indicating that the similar nanostructure determined the comparable texture properties. Gas chromatography-mass spectrometry analysis showed that 0.4% BML decreased the amount of hexanal, hexadecane, 1-octen-3-ol and 2,6,10,14-tetramethylpentadecane but increased the ratio of heptadecane from 18.14 to 38.23% in the treated fish balls, making the flavour of 0.4% BML-treated GP fish balls similar to that of YF balls. Overall, the results suggest that 0.4% BML-tenderised GP could be a promising alternative to YF to produce quality fish balls.

Application of atomic force microscopy in food microorganisms

Background: Microorganisms play an important role in the food industry. Knowledge of the surface ... more Background: Microorganisms play an important role in the food industry. Knowledge of the surface structural and physical properties of food microorganism cells is crucial to gain a detailed understanding of their functions in the natural environment and to explore them efficiently in various food processes. Atomic force microscopy (AFM), as a non-invasive examination tool, has been widely used to image the surface ultrastructure and to probe the physical properties of food microorganisms. Scope and approach: In the current review, detailed applications of AFM in various food microorganisms are outlined, including surface imaging, biomolecular interactions, surface stiffness, and physicochemical properties , which have contributed to our knowledge of cell surface functions. The study emphasises the combination of AFM imaging with force determination, which added a new feature to the AFM technique; i.e., mapping of specific interactions. The combined use of AFM with other complementary techniques for a comprehensive description of cell surface is also reported. Conclusions: and key findings: AFM has given promising results and thus could be a powerful technique for surface characterisation at nanoscale resolution and could provide new insight into the structure-function relationship of microbial surfaces.

Accepted Manuscript Effects of κ-carrageenan on the structure and rheological properties of fish gelatin

Effects of κ-carrageenan on the structure and rheological properties of fish gelatin,

Impact of soybean protein isolate-chitosan edible coating on the softening of apricot fruit during storage

A soybean protein isolate (SPI)-chitosan edible coating was used to prolong the shelf life of apr... more A soybean protein isolate (SPI)-chitosan edible coating was used to prolong the shelf life of apricots stored at 2 °C. Apricots were coated with two different coating formulations (SPI and SPI combined with chitosan). The changes to several parameters including weight loss, firmness, titratable acidity, soluble solids content, pectin contents, and the nanostructural properties of pectin were investigated to evaluate the effectiveness of the coatings. The coatings, especially the SPI-chitosan coating, significantly decreased the weight loss of apricots. Meanwhile, this treatment prevented the decrease in firmness and benefited the textural properties of the tissue. The atomic force microscopy (AFM) results showed a greater F q (the percent of pectin chains of particular width or length among all the chains observed by AFM) for the width and length of pectin molecules in the SPI-chitosan coated samples (width ≥ 61 nm; length ≥ 3 μm), which indicated that the SPI-chitosan coating could inhibit pectin degradation. The results showed that the SPI-chitosan coating is an effective method to preserve the quality of apricots.

Effects of Vacuum Impregnation with Calcium Ascorbate and Disodium Stannous Citrate on Chinese Red Bayberry

This study aimed to improve the shelf life of Chinese red bayberries using vacuum impregnation. V... more This study aimed to improve the shelf life of Chinese red bayberries using vacuum impregnation. Vacuum pressure of 5 kPa for 15 min, atmospheric pressure for 10 min, an impregnation temperature of 20 °C, alone or in combination with isotonic sucrose solution, 1% food-grade disodium stannous citrate (DSC) and 2% food-grade calcium ascorbate were used for vacuum impreg-nation. Quality parameters, including firmness, weight loss, decay rate, microbial counts and polyphenol oxidase (PPO) and peroxidase (POD) activities, of red bayberries were studied at 2 °C for 10 days. The monosaccharide components, chemical structures and nanostructure properties of chelate-soluble pectin (CSP) were further studied using high-performance liquid chromatography, Fourier transform infrared spectroscopy and atomic force microscopy (AFM). The results indicated that vacuum impregnation with calcium ascorbate alone or calcium ascorbate combined with DSC showed significant effects on inhibiting the decrease of firmness (4–10 days), the increase of weight loss (2–10 days), decay rate (4–10 days) and microbial growth (2–10 days). In addition, vacuum impregnation with single calcium ascorbate or DSC or their combination significantly inhibited the increase of colour difference from day 6 to day 10 during storage, which was better than atmospheric impregnation. Furthermore, vacuum impregnation with DSC and calcium ascorbate had the best effect on sensory attributes. The nanostructure analysis by AFM showed CSP of large width and length when calcium ascorbate was impregnated, suggesting that vacuum impregnated with 2% calcium ascorbate inhibited the degradation and dissociation of CSP, although these fruits showed more branching of rhamnogalacturonan and a small change in chemical structure.

sup-0002-FigS2.doc

Structural Modification of Fish Gelatin by the Addition of Gellan, κ-Carrageenan, and Salts Mimics the Critical Physicochemical Properties of Pork Gelatin

Pork gelatin is not suitable for halal and kosher application; however, fish gelatin (FG) can be ... more Pork gelatin is not suitable for halal and kosher application; however, fish gelatin (FG) can be modified for use as a pork gelatin (PG) mimetic. Herein, low-acyl gellan (GE), κ-carrageenan (KC), and salts (CaCl 2 or KCl) were combined with a 180 Bloom tilapia FG. A formulation comprising 5.925% (w/v) FG + 0.025% (w/v) GE + 3mM CaCl 2 best matched the physicochemical properties of PG. The modification increased the FG gel strength from 115 ± 2 to 149 ± 2g (matching the 148 ± 2 of PG), while the T m increased from 27.9 ± 1.0 to 32.4 ± 0.8 °C (matching the 33.1 ± 0.3 °C of PG). Nanoaggregates (diameter between 150 and 300 nm) could be an important structural factor affecting the physicochemical properties, as both PG and GE-modified FG showed a similar frequency distribution in this size group (57.4 ± 1.6% (PG) compared with 56.3 ± 2.2% (modified FG)). To further explore the differences between KC and GE in modifying of FG's structure, the FG-KC and FG-GE gels were compared. The zeta potential and Fourier transform infrared (FTIR) spectroscopy results for the FG-KC gel supported an associative interaction with complex formation, as indicated from the large aggregates and amorphous phase under atomic force microscopy (AFM). Contrastingly, a segregative FG-GE interaction took place in presence of CaCl 2. These structures and interaction differences between FG-GE and FG-KC influenced the macro-properties of FG, possibly explaining the differences in the modification of the melting temperature of FG. A diagram representing the interaction-structure-physicochemical properties was proposed to explain the differences between the FG-GE and FG-KC gels. Practical Application: Certain people cannot consume any pork product or derivatives for religious reasons, thus it is essential to find a pork gelatin (PG) substitute for food product development. The commonly used polysaccharides, gellan and carrageenan, together with salt, can be added to fish gelatin (FG) to match the textural properties of PG, representing a promising substitute for PG. The difference in the mechanism of gellan and carrageenan to improve properties of FG has been revealed from nanostructure level. The use of food grade ingredients and simple mixing process are favorable in the food industry.

sup-0001-FigS1.doc

Characterisation of rheology and microstructures of κ-carrageenan in ethanol-water mixtures

A B S T R A C T The effects of ethanol (up to 20 wt%) on the rheological properties and structura... more A B S T R A C T The effects of ethanol (up to 20 wt%) on the rheological properties and structural characteristics of κ-carra-geenan gel were investigated by Field Emission Scanning Electron Microscopy (FESEM) and Small Angle X-ray Scattering (SAXS). Both the sol-gel and gel-sol transition temperatures shifted to higher degree (from 36.8 ± 0.5 to 52.5 ± 1.4 °C and from 51.2 ± 0.6 to 67.0 ± 0.5 °C, respectively) upon 20 wt% ethanol addition (P < 0.05). The critical relaxation exponent n and the critical gel strength S g obtained from Winter-Chambon criterion decreased and increased, respectively as the ethanol concentration increased. The κ-carrageenan gel was formed due to the formation of fibrillar networks, and the fibrillar density increased upon ethanol addition via FESEM. Moreover, upon 20 wt% ethanol addition, the average radius of gyration of κ-carrageenan strand increased from 1.18 ± 0.03 of control to 1.55 ± 0.02 nm by SAXS. A mechanism underlying the effect of ethanol on the κ-carrageenan gelation was proposed based on coil to double helix transition followed by the helix aggregation.

Effect of ultrasonic pretreatment on whey protein hydrolysis by alcalase: Thermodynamic parameters, physicochemical properties and bioactivities

A B S T R A C T The effects of ultrasonic pretreatment on the enzymolysis thermodynamics and phys... more A B S T R A C T The effects of ultrasonic pretreatment on the enzymolysis thermodynamics and physicochemical properties of whey protein, and the mechanisms behind those effects, were investigated. Changes in the angiotensin-I converting enzyme (ACE) inhibitory and immunomodulatory activities of whey protein hydrolysates after ultrasonic pretreatment were also determined. Results showed that the ultrasonicated whey protein had a higher in degree of hydrolysis than the non-sonicated protein. After the pretreatment, the activation energy (E a), enthalpy of activation (ΔH) and entropy of activation (ΔS) of whey protein enzymolysis were decreased by 15.9%, 16.8%, and 16.4%, respectively. There was no significant change in free energy (ΔG) (P > 0.05). Physicochemical analysis revealed that ultrasound had induced unfolding of the whey protein, resulting in a 43.7% increase in its surface free sulfhydryl content and a 62.6% increase in surface hydrophobicity. Ultrasound significantly decreased the protein's α-helical content and significantly increased its β-sheets and β-turns (P < 0.05). The ACE inhibitory and immunomodulatory activities of the whey protein hydrolysates were significantly increased by ultrasonic pretreatment (P < 0.05). These results suggest that ultrasound can be applied to enhance whey protein enzymolysis for the generation of novel bioactive peptides that can be used as drug or functional food ingredient.

Development of Portable Flow-Through Electrochemical Sanitizing Unit to Generate Near Neutral Electrolyzed Water

We developed a portable flow-through, electrochemical sanitizing unit to produce near neutral pH ... more We developed a portable flow-through, electrochemical sanitizing unit to produce near neutral pH electrolyzed water (producing NEW). Two methods of redirecting cathode yields back to the anode chamber and redirecting anode yields the cathode chamber were used. The NEW yields were evaluated, including: free available chlorine (FAC), oxidation-reduction potential (ORP), and pH. The performances of 2 electrodes (RuO 2-IrO 2 /TiO 2 and IrO 2-Ta 2 O 5 /TiO 2) were investigated. The unit produced NEW at pH 6.46 to 7.17, an ORP of 805.5 to 895.8 mV, and FAC of 3.7 to 82.0 mg/L. The NEW produced by redirecting cathode yields had stronger bactericidal effects than the NEW produced by redirecting anode yields or NEW produced by mixing the commercial unit's anode and cathode product (P < 0.05). Electron spin resonance results showed hydroxyl free radicals and superoxide anion free radicals were present in the NEW produced by developed unit. The NEW generator is a promising sanitizing unit for consumers and the food industry to control foodborne pathogens. Practical Application: Current commercial NEW-producing units are quite large and are not convenient for family using. The developed portable flow-through, NEW-producing unit has great potential in a wide range of applications, such as organic farm, households, and small food industries. The examined sanitizing treatments showed effective control of Escherichia coli O157:H7 and Listeria monocytogenes.

Metabolite profiling of Listeria innocua for unravelling the inactivation mechanism of electrolysed water by nuclear magnetic resonance spectroscopy

A B S T R A C T Bactericidal effects of low concentration electrolysed water (LcEW) on microorgan... more A B S T R A C T Bactericidal effects of low concentration electrolysed water (LcEW) on microorganisms are previously well reported ; however, the inactivation mechanism of EW is not understood. The lethal and sublethal injuries of L. monocytogenes and L. innocua by EW treatments were determined and the metabolic profile changes for L. in-nocua were characterised using nuclear magnetic resonance (NMR). Microbial metabolomics approach combined with multivariate data analyses was used to interpret the cellular chemical fingerprints of L. innocua. The relative amount of intracellular reactive oxygen species (ROS) was assayed using 2′,7-dichlorodihydrofluorescein dia-cetate (H 2 DCFDA). The results showed that the proportion of the sublethally injured microbial cells L. mono-cytogenes and L. innocua increased from 40% to 70% and from 35% to 65%, respectively, when the free available chlorine (FAC) of LcEW increased from 2 to 8 mg/L. Overall, 36 low-molecular-weight metabolic compounds in L. innocua extracts were characterised by NMR spectroscopy. EW perturbation resulted in a drastic and multitude disruption across a wide range of biochemical process including peptidoglycan synthesis, nucleotides bio-synthesis and amino acid metabolism. Elevated levels of α-ketoglutarate and succinate implicated the enhanced glutamate decarboxylase (GAD) system and γ-aminobutyric acid (GABA) shunt for the protection against oxi-dative stress. These findings provided the comprehensive insights into the metabolic response of Listeria to EW oxidative stress and can serve as a basis for better utilisation for sanitisation.

Effect of exogenous ATP on the postharvest properties and pectin degradation of mung bean sprouts (Vigna radiata

A B S T R A C T The effects of exogenous ATP on the postharvest quality, browning and softening o... more A B S T R A C T The effects of exogenous ATP on the postharvest quality, browning and softening of mung bean (Vigna radiata) sprouts were evaluated. ATP treatment significantly alleviated the quality loss and browning events during the storage of 3 days. It also reduced the oxidant damage by inducing high activities of peroxidase (9.3–13.9%) and superoxide dismutase (8.8–10.3%) which scavenged the reactive oxygen species (ROS) effectively. Transcriptional results indicated that ATP treatment decreased VrPL1, VrPME and VrPG1 gene expression levels more than 2 folds at some time points. Furthermore, the atomic force microscope (AFM) images revealed that the pectin degradation was notably slowed by ATP treatment and the width and height of pectin backbone were better maintained (47.1% and 45.6% higher than control without ATP treatment). The cooperative effects of ROS scavenging and decreased expressions of pectin-related genes might contribute to the deferred pectin deterioration and firmness loss by ATP treatment.

Colourimetric detection of swine-specific DNA for halal authentication using gold nanoparticles

Detecting pork contamination is critical for halal food preparation. A fragment of species-specif... more Detecting pork contamination is critical for halal food preparation. A fragment of species-specific DNA from swine mitochondrial genome was selected as a target, and two oligonucleotides complementary to the target were used as probes for pork identification. The probe-conjugated gold nanoparticles bound to the target DNA, leading to the aggregation of gold nanoparticles and thus causing the colour of the gold nanoparticles to change from red to blue. More than 0.1 mmol/L of DNA led to an obvious colour change, which was observed by naked eyes after dotting test solutions onto a thin layer chromatography (TLC) plate. Furthermore, 0.001e1 mmol/L of the target was semi-quantified by using a digital camera and image processing software. This colourimetric detection might be a promising technique for differentiation of pork from other animal meat products without using any sophisticated machines, and thus will be used for halal authentication.

Effects of sucrose addition on the rheology and microstructure of k-carrageenan gel

The thermoreversible gelation behaviour of aqueous k-carrageenan solution with addition of sucros... more The thermoreversible gelation behaviour of aqueous k-carrageenan solution with addition of sucrose (up to 30 wt%) was investigated via small and large deformation oscillatory rheology. The structures of these k-carrageenan/sucrose gels were characterised by Fourier transform infrared (FTIR) spectroscopy, small angle X-ray scattering (SAXS) and field emission scanning electron microscopy (FESEM). Incorporation of 30 wt% sucrose shifted both the gelation temperature (from 36.8 C to 52.8 C) and melting temperature (from 51.2 C to 67.3 C) to a higher level and made gel network stronger. The critical relaxation exponent n, critical gel strength S g and normalised S g obtained from Winter-Chambon equation varied as the concentration of sucrose increased. More specifically, with an increased addition of sucrose, n decreased while both S g and normalised S g increased. The shift of FTIR band of G4S in k-carrageenan and loss of the vibration band of free hydroxyl group in sucrose indicated the interactions between sucrose and k-carrageenan molecules. SAXS and FESEM results supported the rheology findings and revealed that denser and thicker carrageenan fibril structures formed when addition of sucrose increased. Moreover, upon 30 wt% sucrose, the average cross-sectional radius of gyration R c of the carrageenan chains increased from 1.17 to 1.47 nm. In summary, a scheme was proposed to demonstrate how sucrose addition promoted the gelation of k-carrageenan by facilitating the formation of denser and thicker fibril helical junctions.

Comparative study of pyrethroids residue in fruit peels and fleshes using polystyrene-coated magnetic nanoparticles based clean-up techniques

An efficient and rapid method for quantifying pyrethroids pesticide residue in fruits samples was... more An efficient and rapid method for quantifying pyrethroids pesticide residue in fruits samples was developed in the present study. The application of lab prepared polystyrene magnetic nanoparticles based magnetic solid phase extraction technique combined with liquid-solid extraction helped clean-up the sample and preconcentrate the targeted analytes prior to HPLC quantification. The lab prepared nanoparticles were characterised with Fourier transform infrared spectroscopy, atomic force microscopy, X-ray diffraction spectroscopy, as well as vibrating sample magnetometer to study their size, morphology, crystal structure, functional groups and magnetism properties, respectively. Afterwards, optimisation of the parameters affecting extraction efficiency was carried out in order to achieve optimum conditions for extracting pyrethroids residue from fruit samples. Analytical performances were evaluated by carrying out experiments at optimum conditions. Results showed that the limit of detection and limit of quantification were below 0.1445 and 0.5116 ng g À1 , respectively for the six pyrethroids tested. The recovery rates were within the range of 73.6%e123.1% with intra-day and inter-day relative standard deviation being less than 16.5% and 15.4%, respectively, suggesting satisfactory reproducibility of the proposed method. Real sample analysis was performed using 6 kinds of commonly consumed fruits obtained from local supermarkets in Singapore, including apples, pears, oranges, lemons, grapes and nectarines. The peel and flesh were tested separately to study the difference of pyrethroids residue in different parts of fruits. The grape sample tested was detected with permethrin residue on its peel. There was no violation since the permethrin amount detected was way much lower than the maximum residue limit set by local government.

39-Figs S1-S3.docx

Supplementary Figure 1. ESI-MS and ESI-MS 2 spectra of two purified monomeric anthocyanins. Struc... more

Characterization and purification of anthocyanins from black peanut (Arachis hypogaea L.) skin by combined column chromatography

Journal of Chromatography A, 2017

Cyanidin-3-O-sambubioside Preparative ODS-AQ column HPLC-PDA-ESI–MS/MS NMR spectroscopy a b s t r... more Cyanidin-3-O-sambubioside Preparative ODS-AQ column HPLC-PDA-ESI–MS/MS NMR spectroscopy a b s t r a c t Black peanut skins as a byproduct from peanut industry contain abundant anthocyanins, evaluated as 8.61 ± 0.27 mg/g dry black peanut skins, are currently poorly exploited. In this work, four anthocyanins and three major flavonols were detected and identified by HPLC-PDA-ESI–MS/MS from the acidified water extract of black peanut skins of Arachis hypogaea L. After preliminary removal of flavonols by ethyl acetate (EtOAc), further purification of the anthocyanins was conducted using a combination of Amberlite XAD-7HP and ODS-AQ-HG column chromatography methods. Two most abundant monomeric anthocyanins cyanidin-3-O-sophoroside (5.77 ± 0.42 mg) and cyanidin-3-O-sambubioside (4.10 ± 0.17 mg) were eventually obtained from 2 g dry black peanut skins, and their purities were determined by HPLC-PDA as 97.29% and 98.28% at the yields of 87.47% and 64.27% on the basis of their total amount in the crude extracts, respectively. These sequential treatments can be easily adapted to large-scale fractionation of pure anthocyanin monomers.

Influence of chitosan-based coatings on the physicochemical properties and pectin nanostructure of Chinese cherry

A B S T R A C T The effects of chitosan-based coatings on the postharvest performance Chinese che... more A B S T R A C T The effects of chitosan-based coatings on the postharvest performance Chinese cherry during a twenty days storage period were investigated. The chitosan-based coatings effectively delayed postharvest ripening parameters including weight loss, decay rate, firmness, soluble solid content (SSC) and titratable acidity (TA). The most effective treatment was a combined chitosan and nano-SiOx coating, which led to 51% less weight loss, 32% less decay rate, 57% more firmness, and less SSC and TA content changes than the control group. This combined coating also maintained a higher content of sodium carbonate-soluble pectin (SSP), and inhibited pectin chain degradation. Qualitative and quantitative analysis revealed that the firmness of fruit was closely related to nanostructural morphologies and SSP chain width. In addition, modifications of SSP were correlated with fruit softening, especially SSP polymers and branched chains. These results demonstrate the effect of chitosan and nano-SiOx coating on extending the shelf life of Chinese cherries during postharvest storage.

Effects of Bromelain Tenderisation on Myofibrillar Proteins, Texture and Flavour of Fish Balls Prepared from Golden Pomfret

An enzymatic method to tenderise golden pomfret (GP, Trachinotus blochii) flesh by marinating wit... more An enzymatic method to tenderise golden pomfret (GP, Trachinotus blochii) flesh by marinating with bromelain (BML) solution was developed to produce GP fish balls with a texture similar to those of yellowtail fusilier (YF, Caesio cuning). Treatment with BML reduced the hardness, chewiness and gel strength significantly but increased the resilience of GP fish balls. As a result, 0.4% (enzyme-substrate ratio, w/w) BML-treated GP fish balls had the same texture properties as YF fish balls. Meanwhile, changes in myofibril-lar proteins in the fish balls were determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis, matrix-assisted laser desorption/ionisation time-of-flight mass spec-trometry and atomic force microscopy. The results indicated that BML degraded myosin light chain and troponin T effectively , without affecting actin. BML treatment generated protein fragments with significantly smaller sizes, thereby improving the tenderness of the flesh. The length, width and height of the myofibrils from 0.4% BML-treated fish ball were 6.42, 1.52 and 1.48 μm, respectively, which were not significantly different from the myofibrils of YF fish balls, indicating that the similar nanostructure determined the comparable texture properties. Gas chromatography-mass spectrometry analysis showed that 0.4% BML decreased the amount of hexanal, hexadecane, 1-octen-3-ol and 2,6,10,14-tetramethylpentadecane but increased the ratio of heptadecane from 18.14 to 38.23% in the treated fish balls, making the flavour of 0.4% BML-treated GP fish balls similar to that of YF balls. Overall, the results suggest that 0.4% BML-tenderised GP could be a promising alternative to YF to produce quality fish balls.

Atomic Force Microscopy (AFM): Principles, Modes of Operation and Limitations

Polymer Morphology

Design Online Virtual Laboratory Exercises and an Interactive Platform for Learning Food Processing and Engineering

Teaching Enhancement Grant (AY2013/2014)-Improving Problem-based Learning with Stuent Tutors in a Course of Food Product Development and Packaging

Book-Atomic Force Microscopy (AFM): Principles, Modes of Operation and Limitations